Data storage devices that read data from and write data to data storage discs include an apparatus that writes the data on the disc, reads the data from the disc, or performs both functions. Because of the high density of data stored on a data storage disc such as an optical or electromagnetic disc, the reading or writing element should be carefully constructed and should be tested to ascertain whether it performs up to standards of quality.
Prior to attaching a head gimbal assembly (HGA) into a hard disc drive, for example, it is desirable to dynamically test the functionality of the read and write transducers that reside on the HGA so that a defective HGA may be identified and sorted. Such testing can include preliminary activities to align, configure, and prepare the HGA for testing, followed by the actual electrical test of the HGA. Because an HGA is typically small, fragile, and contains sensitive electronic components, it is susceptible to mechanical stress, electro-static discharge, environmental contamination, and other handling-related issues. To avoid these handling-related issues, current systems mount the HGA on an intermediate mounting fixture that supports the HGA throughout the testing process.
Testing of the HGA typically includes reading from and writing to a test disc. The test disc can include servo tracks or servo patterns. Servo tracks and servo patterns are position information located at pre-selected sites on the disc. This position information can be used by an HGA controller to identify the location of the HGA's transducer with respect to the disc, to control HGA motion and to regulate HGA position so that reading or writing can be performed in the proper place. The test disc may further include data other than position information.
Data on a data storage disc is typically arranged concentrically or spirally around a central point. The location of the central point depends upon the data or the tracks on the disc, which is not necessarily coincident with the geometric center of the disc. When the disc is mounted upon a spindle for rotation, the disc is rotated about an axis of the spindle. As a practical matter, data written on the disc is eccentric with respect to the disc, and therefore, the data will also be eccentric with respect to the spindle axis. The motion control system holding the HGA reading data from or writing data to such a disc may have to compensate for the eccentricity. During testing of HGAs, it may be desirable to reduce the eccentricity so that eccentricity does not interfere with the testing, so that compensation for eccentricity is of no important consequence.